1. Field of the Invention
The present invention relates to a signal processing apparatus for a stringed instrument, the apparatus mixing a signal acquired by picking up a vibration of a string, and a signal corresponding to an instrument sound including a resonance of a body caused by the vibration of the string.
2. Description of the Related Art
When a player plays an acoustic guitar, its volume is limited. Therefore, when the player plays an acoustic guitar live in a big hall, sound is collected and amplified by use of a microphone to increase volume. When there is the other instrument near the acoustic guitar, the sound of the other instrument might be picked up, or acoustic feedback might be caused in this method. In order to prevent this situation, a pickup sensor composed of a piezoelectric element is mounted to a saddle supporting a string for converting the vibration of the string into an electric signal, and the electric signal is amplified to increase volume.
The electric signal (pickup signal) corresponding to the vibration of the string can be acquired by mounting the pickup sensor to the saddle. However, the pickup signal includes few components involved with a resonance of a body called “box resonance”. Therefore, as described in Japanese Unexamined Patent Publication No. 2011-197325 and illustrated in FIG. 11, there has conventionally been known a technique in which a pickup signal mainly corresponding to a vibration of a string and picked up by a pickup sensor 1, mounted to a saddle supporting the string, is fed to an adder 2, the pickup signal picked up by the pickup sensor 1 is fed to the adder 2 via a FIR (Finite Impulse Response) filter 3 that is used to add a resonance component of a body, the fed two signals are mixed by the adder 2 to complement the resonance component of the body that is reduced, and the resultant is outputted. In this case, the FIR filter 3 performs a convolution operation to the input signal to simulate the resonance caused by the resonance of the body of the stringed instrument, thereby generating an instrument sound signal sufficiently including the resonance component. Accordingly, the signal mainly corresponding to the vibration of the string of the stringed instrument and the signal corresponding to the instrument sound signal sufficiently including the body resonance caused by the vibration of the string are mixed, whereby a stringed instrument sound satisfactorily reflecting the body resonance in addition to the string vibration is outputted.